There is known a method for damping a vehicle body sprung mass vibration in an automobile, in particular, pitching vibration by torque control of an internal combustion engine. Hereinafter, torque control of an internal combustion engine for this purpose will be especially called sprung mass vibration damping control. In the sprung mass vibration damping control, the pitching vibration corresponding to a present driving force is obtained from a vehicle body sprung mass vibration model, and vibrational correction torque which cancels out the pitching vibration is calculated. Subsequently, basic required torque calculated from an accelerator opening is corrected according to the correction torque, and the output torque of the internal combustion engine is controlled in accordance with the required torque after correction. More specifically, in sprung mass vibration damping control, the torque which is outputted by an internal combustion engine is vibrationally changed.
Torque control in an internal combustion engine, in particular, torque control in the case of a gasoline engine is generally performed by controlling an intake air quantity by operation of a throttle. When torque is to be vibrationally changed, the throttle can be vibrationally moved to increase and decrease the intake air quantity actively. However, there is a delay in response of the intake air quantity to the operation of the throttle, and therefore, required torque cannot be always realized with high responsiveness. For example, when the required torque includes a high-frequency component as in the aforementioned sprung mass vibration damping control, a desired high-frequency component is difficult to create by only the control of the intake air quantity, and the required torque is unlikely to be realized with high precision.
As above, with only the control of the intake air quantity by operation of a throttle, the range of the realizable required torque is narrow, and there is the fear that the required torque cannot be completely realized. In order to realize the required torque including a high-frequency component with high precision, torque control by the actuator with torque responsiveness higher than a throttle is required. In regard with this point, Japanese Patent Laid-Open No. 2009-068430 describes the method for performing torque control by cooperatively operating a throttle and an ignition device. According to the method described in the publication, a target air quantity is determined based on the required torque, and a throttle opening is calculated from the target air quantity with use of an inverse model of an air model. Further, in parallel with this, estimation torque which is achieved with the present throttle opening is calculated, and a correction amount of ignition timing is determined in accordance with the difference of the required torque and the estimation torque.
According to the method described in Japanese Patent Laid-Open No. 2009-068430, when the required torque cannot be realized by only control of the intake air quantity by operation of the throttle, the excess or deficiency can be compensated by correction of the ignition timing. Torque control by operation of an ignition device is extremely high in responsiveness of torque as compared with that by operation of a throttle. Consequently, it is conceivable that according to the method described in the aforesaid publication, even if a high-frequency component is included in the required torque as in the aforementioned sprung mass vibration damping control, the required torque can be realized with high precision.
However, a problem also exists in the method described in the aforesaid publication. When retardation of the ignition timing is frequently performed in accordance with the high-frequency component of the required torque, the fuel consumption performance is worsened due to reduction of efficiency. Fuel consumption performance is one of the important performances required of automobiles similarly to improvement of drivability which is the object of sprung mass vibration damping control. Accordingly, increasing achievability of the required torque so as not to impair the fuel consumption performance is required of torque control, in particular, sprung mass vibration damping control of an internal combustion engine.
Incidentally, in the case of a spark ignition type internal combustion engine like a gasoline engine, an air-fuel ratio is also closely related to the torque which is generated by the internal combustion engine, in addition to an intake air quantity and ignition timing. Therefore, as is described in, for example, Japanese Patent Laid-Open No. 11-82090, there is known the method for controlling an intake air quantity, a fuel injection amount and ignition timing in accordance with target torque and a target air-fuel ratio. Further, as is described in Japanese Patent Laid-Open No. 9-240322, there is also known the art of controlling an air-fuel ratio in accordance with the magnitude of the torque generated by an internal combustion engine.
In the method descried in Japanese Patent Laid-Open No. 11-82090, a target air-fuel ratio is determined from the operation conditions such as a water temperature and an atmospheric pressure, and from the target torque and the target air-fuel ratio, a target intake air quantity, a target fuel injection amount and target ignition timing are calculated. According to the method, torque control can be performed by using not only an intake air quantity and ignition timing, but also a fuel injection amount, and therefore, the realization range of the required torque is considered to be more widened.
However, there is a large difference between response of an actual intake air quantity to a change of a target intake air quantity, and response of an actual fuel injection amount to a change of a target fuel injection amount. Therefore, in the method described in Japanese Patent Laid-Open No. 11-82090, a deviation occurs between the target air-fuel ratio and the actual air-fuel ratio in a transitional state in which the air quantity changes. As a result, a deviation also occurs between the required torque and the actual generation torque. Further, the target ignition timing is determined from a map of the air quantity and an engine speed, and therefore, the excess or deficiency amount with respect to the required torque cannot be compensated by correction of ignition timing. Accordingly, it has to be said that with the method described in the aforementioned Japanese Patent Laid-Open No. 11-82090, the required torque including a high-frequency component is difficult to realize highly precisely with high responsiveness.